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Valley Forge National Historical Park is an oasis of open space consisting of 3500 acres (1416ha) of fields and forest surrounded by residential development and transportation corridors. The vegetation within the park is influenced by many factors, especially the underlying geology, the Schuylkill River and human activity. The underlying bedrock is composed of three primary types: red sandstone and shale along the river associated with low, rolling, hilly topography; dolostone, a carbonate rock, dominating the southern half of the park and underlying gently rolling terrain and sinkholes; and smaller patches of quartzite, a very hard and erosion resistant rock, in the western part of the park (e.g. at Mt. Misery and Mt. Joy). The quartzite and quartz schist that make up Mt. Misery result in well-drained soils and therefore support drought tolerant plant community types on the upper slopes. The soils on the east slopes of Mt. Misery support Dry Oak Hardwood Forests, consisting of chestnut oak, black oak, white oak, and/or scarlet oak. The red sandstone and shale formations create fertile soils, which are more suitable for agriculture. Such areas consist of open grasslands, shrublands, croplands, tree plantations and young successional forests. The Schuylkill River and Valley Creek run through the park as well. The Schuylkill River floodplain has deep, rich soils that support several types of floodplain forest, such as Riverine Floodplain Forest and Silver Maple Floodplain Forest, some of which are heavily infested with invasive and/or exotic plant species. The Riverine Floodplain forest consists of silver maple, green ash, sycamore, box elder, spicebush, false nettle, and stiltgrass. Along the river in the northwest corner of the park, the floodplain was drastically altered by the construction of a large dike, resulting in a very narrow floodplain in this area. North of the dike is foundopen and forested wetlands. Drier areas support grasslands and successional forests. Two types of wetlands occur naturally within the park: one type is an open, non-forested wetland dominated by reed canary grass (Phalaris arundinacea) and wetland species such as rice cut-grass (Leersia oryzoides) and burreed (Sparganium spp.). This wetland type is called Wet Meadow. The other type of wetland is called Skunk Cabbage Seepage Meadow, and occurs in forested settings with a partial to closed canopy. The herbaceous layer is dominated by skunk cabbage (Symplocarpus foetidus). Meadows encourage the growth of native vegetation and provide a good habitat for flowers, such as purple top and little blue stem, and wildlife, such as foxes, deer, hawks, meadowlarks, and an assortment of butterflies. Other natural and semi-natural plant communities occurring within the part are Tuliptree Forests and Northeastern Modified Successional Forest, in which the canopy is often dominated by black walnut, white ash, tree-of-heaven, and/or black locust. This forest type is often characterized by conspicuous vine cover in the tree layer including plants such as oriental bittersweet, Japanese honeysuckle, and summer grape.
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